Since a paradigm of a wireless communication service has been changed from a voice service to a multimedia service, the orthogonal frequency division multiplexing (OFDM) scheme and the orthogonal frequency division multiplexing access (OFDMA) scheme using the OFDM scheme has received a great deal of attention. Since the OFDM scheme has a good bandwidth-efficiency and characteristics that are robust against multipath fading, it is widely used in a fourth generation mobile communication system, a digital multimedia broadcasting TV, and a wireless local area network (WLAN).
A signal transmitting device and a signal receiving device in a conventional OFDM scheme will be described with reference to FIG. 1.
FIG. 1 shows a block diagram of a signal transmitting device 10 and a signal receiving device 20 in the conventional OFDM scheme.
As shown in FIG. 1, the signal transmitting device 10 in the conventional OFDM scheme includes a digital modulating unit 11, a serial to parallel converter (SPC) 12, an inverse fast Fourier transform (IFFT) unit 13, a parallel to serial converter (PSC) 14, a cyclic prefix (CP) adder 15, a digital to analog converter (DAC) 16, a transmitting unit 17, and a transmitting antenna 18.
The digital modulating unit 11 performs digital modulating operations including binary phase shift keying (BPSK), quadrature amplitude modulation (QAM), 16-QAM, and 64-QAM for a data symbol that is binary data to be transmitted to a channel, and generates a digital-modulated symbol. The digital modulating unit 11 may be referred to as a “symbol mapping unit”.
The SPC 12 serially receives a plurality of digital-modulated symbols from the digital modulating unit 11 and outputs them in parallel.
The IFFT unit 13 performs an IFFT operation for the plurality of parallel digital-modulated symbols output from the SPC 12, and generates a plurality of IFFT symbols.
The PSC 14 serially outputs the plurality of parallel IFFT symbols output from the IFFT unit 13.
The CP adder 15 adds a signal, which is referred as a cyclic prefix, to a former part of the plurality of serial IFFT symbols, which is output from the PSC 14, and generates a symbol group including the CP signal. Here, the CP is a part of symbols in a latter part of the plurality of IFFT symbols.
The DAC 16 receives the symbol group including the CP from the CP adder 15, and converts the symbol group into one analog OFDM symbol.
The transmitting unit 17 amplifies the generated OFDM symbol to a radio frequency (RF) signal, and transmits the RF signal to a channel through the transmitting antenna 18.
As shown in FIG. 1, the signal receiving device 20 in the conventional OFDM scheme includes a receiving antenna 21, a receiving unit 22, an analog to digital converter (ADC) 23, a cyclic prefix (CP) eliminating unit 24, an SPC 25, a fast Fourier transform (FFT) unit 26, a PSC 27, and a digital demodulating unit 28.
The receiving unit 22 receives the OFDM symbol from the channel through the receiving antenna 21.
The ADC 23 converts the OFDM symbol into a plurality of digital symbols.
The CP eliminating unit 24 eliminates the CP from the plurality of digital symbols.
The SPC 25 serially receives the plurality of CP-eliminated digital symbols, and outputs them in parallel.
The FFT unit 26 receives the plurality of parallel symbols from the SPC 25, performs a fast Fourier transform (FFT) operation, and generates a plurality of frequency domain symbols.
The PSC 27 receives the plurality of symbols from the FFT unit 26 in parallel, and serially outputs them.
The digital demodulating unit 28 digitally demodulates the plurality of symbols serially output from the PSC 27, and generates a final data symbol.
The above OFDM symbol problematically has a large peak to average power ratio (PAPR). A signal is distorted in the OFDM symbol having the large PAPR while it is amplified by nonlinear devices including a high power amplifier (HPF).
Accordingly, various studies have been ongoing to improve the PAPR characteristic. However, since a part of subcarriers are used to improve the PAPR in suggested methods, the data transmission speed is reduced.